#1 Toby Alderweireld
The Belgian is one of the best central defenders in the Premier League at the moment; his reading of the game along with his ball playing abilities are exceptional. At Tottenham, he has formed a formidable partnership with Sanchez and Vertonghen in defense, and helped the club finish in the top four in back-to-back seasons.
Alderweireld started his club career with Ajax before moving to Atletico Madrid, where he won the La Liga and reached the UEFA Champions League final in his debut season. The Belgian then spent a season-long loan at Southampton before moving to Tottenham Hotspur in 2015.
Mourinho reportedly wanted Alderweireld in the summer, but the Spurs wanted a player in exchange which the United board refused to agree with. However, there are contract disputes between the player and the club at the moment, which might see Mourinho finally getting his man in January at a relatively lesser fee.